1. Field of the Invention
The present invention generally relates to an electric-power supplying device, and a control circuit and a controlling method therefor, and more particularly, to an electric-power supplying device comprising switching elements switched according to a switching pulse so as to perform a rectification, and rectifying elements connected in parallel with the switching elements so as to perform a rectification, and a control circuit and a method for controlling the electric-power supplying device.
2. Description of the Related Art
FIG. 1 is a block diagram of an information processing system 1.
The information processing system 1 comprises an alternator 11, an AC-DC converting unit 12, main boards 13-1 to 13-n, and a network 14. The alternator 11 supplies an alternating current voltage (an alternating current) to the AC-DC converting unit 12. The AC-DC converting unit 12 converts the alternating current voltage (the alternating current) into a direct current voltage (a direct current).
The direct current voltage (the direct current) is supplied from the AC-DC converting unit 12 to the main boards 13-1 to 13-n. The main boards 13-1 to 13-n are information processing devices interconnected and intercommunicated via the network 14. Each of the main boards 13-1 to 13-n comprises DC-DC converting units 21-1 to 21-3, a CPU 22, and a storage device 23, and a communication apparatus 24.
The DC-DC converting unit 21-1 generates a predetermined direct current voltage based on the direct current voltage (the direct current) supplied from the AC-DC converting unit 12, and supplies the generated direct current voltage to the CPU 22. The CPU 22 is driven by the direct current voltage supplied from the DC-DC converting unit 21-1 so as to process data. The DC-DC converting unit 21-2 generates a predetermined direct current voltage based on the direct current voltage (the direct current) supplied from the AC-DC converting unit 12, and supplies the generated direct current voltage to the storage device 23. The storage device 23 is driven by the direct current voltage supplied from the DC-DC converting unit 21-2 so as to store the data processed by the CPU 22 and data supplied from the storage device 23. The DC-DC converting unit 21-3 generates a predetermined direct current voltage based on the direct current voltage (the direct current) supplied from the AC-DC converting unit 12, and supplies the generated direct current voltage to the communication apparatus 24. The communication apparatus 24 controls communications with the network 14.
FIG. 2 is a block diagram of the DC-DC converting unit 21-1.
The DC-DC converting unit 21-1 comprises DC-DC converting circuits 31-1 and 31-2, and diodes D1 and D2. The DC-DC converting circuit 31-1 converts the direct current voltage supplied from the AC-DC converting unit 12 into a predetermined voltage. The DC-DC converting circuit 31-1 detects an output current and the output voltage so as regulate the output voltage at a constant level. The output voltage is supplied from the DC-DC converting circuit 31-1 to the CPU 22 via the diode D1. The DC-DC converting circuit 31-2 is arranged in the same manner as the DC-DC converting circuit 31-1 such that the output voltage is supplied from the DC-DC converting circuit 31-2 to the CPU 22 via the diode D2.
In a normal operation, direct currents are supplied from the DC-DC converting circuit 31-1 and the DC-DC converting circuit 31-2 to the CPU 22. Upon rising, when the output voltage of the DC-DC converting circuit 31-1 rises earlier than the output voltage of the DC-DC converting circuit 31-2, the diode D2 keeps the current from flowing from the DC-DC converting circuit 31-1 to the DC-DC converting circuit 31-2. That is, the diode D2 can prevent an adverse current to the DC-DC converting circuit 31-2.
Upon rising, when the output voltage of the DC-DC converting circuit 31-2 rises earlier than the output voltage of the DC-DC converting circuit 31-1, the diode D1 keeps the current from flowing from the DC-DC converting circuit 31-2 to the DC-DC converting circuit 31-1. That is, the diode D1 can prevent an adverse current to the DC-DC converting circuit 31-1.
Next, a more detailed description will be given of the DC-DC converting circuit 31-1 (the DC-DC converting circuit 31-2).
FIG. 3 is a block diagram of the DC-DC converting circuit 31-1.
The DC-DC converting circuit 31-1 comprises an inverter circuit 41, a transformer 42, switching elements (transistors) Q1 and Q2, rectifying elements (diodes) D11 and D12, a control circuit 43, a choke coil L0, an output current detection resistance Rs, and a smoothing capacitor C0.
The direct current voltage is impressed from the AC-DC converting unit 12 to the inverter circuit 41. The inverter circuit 41 converts the direct current voltage impressed from the AC-DC converting unit 12 into an alternating current voltage.
The alternating current voltage converted by the inverter circuit 41 is impressed to a primary coil L1 of the transformer 42. An alternating current in accordance with the alternating current voltage impressed from the inverter circuit 41 flows in the primary coil L1 of the transformer 42 so that a magnetic flux is generated therein in accordance with the flowing current. The magnetic flux generated in the primary coil L1 of the transformer 42 is transmitted to secondary coils L21 and L22 of the transformer 42. A secondary current in accordance with the magnetic flux transmitted from the primary coil L1 flows in the secondary coils L21 and L22.
One end of the secondary coil L21 is grounded via a source and a drain of the transistor Q1, and the other end of the secondary coil L21 is connected to one end of the choke coil L0. One end of the secondary coil L22 is grounded via a source and a drain of the transistor Q2, and the other end of the secondary coil L22 is connected to the one end of the choke coil L0. The transistors Q1 and Q2 are MOS-FETs (Metal-Oxide-Semiconductor field effect transistors), for example.
The transistors Q1 and Q2 have gates connected to the control circuit 43 so as to be switched according to a switching pulse supplied from the control circuit 43. The diode D11 is connected between the source and the drain of the transistor Q1 in parallel. An anode of the diode D11 is grounded via the drain of the transistor Q1, and a cathode of the diode D1 is connected to the secondary coil L21 via the source of the transistor Q1.
The other end of the choke coil L0 is connected to an output terminal Tout via the output current detection resistance Rs. The smoothing capacitor C0 is connected between the output terminal Tout and a ground terminal Tgnd. An electric potential of a node of the secondary coil L21 and the secondary coil L22 is smoothed by the choke coil L0 and the smoothing capacitor C0, and is output via the output terminal Tout.
Voltages at both ends of the output current detection resistance Rs and an output voltage Vout of the output terminal Tout are supplied to the control circuit 43. When the output voltage Vout supplied from the output terminal Tout becomes small, the control circuit 43 reduces a pulse width, or increases cycles, of the switching pulse supplied to the gates of the transistors Q1 and Q2. When the output voltage Vout supplied from the output terminal Tout becomes large, the control circuit 43 enlarges the pulse width, or decreases the cycles, of the switching pulse supplied to the gates of the transistors Q1 and Q2.
Thus, the gates of the transistors Q1 and Q2 are supplied with the switching pulse from the control circuit 43, and the transistors Q1 and Q2 are switched alternately according to the switching pulse supplied from the control circuit 43.
Additionally, the control circuit 43 detects the output current according to the voltages at both ends of the output current detection resistance Rs. When the output current is smaller than a predetermined threshold value, i.e., when a load is light, the control circuit 43 turns off the transistors Q1 and Q2 continually, and performs a diode rectification by using the diodes D11 and D12. Performing the diode rectification eliminates a necessity of performing undue switching so as to reduce electric power loss resulting from the switching.
On the other hand, when the output current is larger than the predetermined threshold value, i.e., when the load is heavy, the transistors Q1 and Q2 are switched according to the switching pulse corresponding to the output voltage Vout so as to perform a synchronous rectification. In performing the synchronous rectification, an on-state voltage of the transistors Q1 and Q2 is approximately 0.01 [V] which is sufficiently small compared to an on-state voltage of the diodes D11 and D12 of approximately 0.7 [V]; accordingly, performing the synchronous rectification alleviates a voltage drop due to the switching elements (the transistors Q1 and Q2) so as to efficiently supply the current to a load (the CPU 22), reducing electric power loss.
However, a conventional electric-power supplying device of a kind as described above (the DC-DC converting circuit 31-1 or the DC-DC converting circuit 31-2) has such problems as a change in output voltage upon switching the synchronous rectification performed by using the switching elements (the transistors Q1 and Q2) and the diode rectification performed by using the rectifying elements (the-diodes D11 and D12) according to a difference-in the voltages at both ends of the on-state resistance (the output current detection resistance RS), as shown in FIG. 4.
When applying an electric-power supplying device of this kind to such an apparatus as a computer, a voltage change needs to be restrained below several tens of millivolts. In order to reduce the change in the output voltage shown in FIG. 4, it is necessary to increase an inductance of the choke coil L0 and a capacitance of the smoothing capacitor C0. Increasing the inductance of the choke coil L0 and the capacitance of the smoothing capacitor C0 reduces the change in the output voltage, as indicated by a broken line shown in FIG. 4. However, increasing the inductance of the choke coil L0 and the capacitance of the smoothing capacitor C0 has such problems as enlarging the electric-power supplying device in size, and increasing costs of thereof.
Additionally, in an electric-power supplying system comprising a redundancy of these electric-power supplying devices, each of the diodes D1 and D2 is connected between the output terminal of the electric-power supplying device (the DC-DC converting circuit 31-1 or the DC-DC converting circuit 31-2) and the load (the CPU 22) such that a direction from the electric-power supplying device to the load becomes a forward direction of the diode. This arrangement has such problems as causing a loss due to the diode, and increasing the number of components and costs thereof.
It is a general object of the present invention to provide an improved and useful electric-power supplying device, and a control circuit and a controlling method therefor, in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an electric-power supplying device capable of supplying electric power efficiently, and a control circuit and a controlling method therefor.
In order to achieve the above-mentioned objects according to the present invention, upon switching between a rectification performed by switching elements switched according to a switching pulse and a rectification performed by rectifying elements connected in parallel with the switching elements, the switching pulse is gradually altered.
According to the present invention, the rectification performed by the switching elements and the rectification performed by the rectifying elements can be smoothly switched so as to reduce a change in an output voltage.
Additionally in the present invention, the rectifying elements may perform the rectification upon turning power supply on, and the switching pulse may be altered gradually after a predetermined period of time elapses since turning the power supply on so as to cause the rectification performed by the rectifying elements to transit gradually to the rectification performed by the switching elements.
According to the present invention, even when a current flows adversely from a load, such as a CPU, upon a rise of an output voltage, the rectifying elements can prevent the adverse current. After the rise of the output voltage, the switching pulse is altered gradually so as to smoothly switch the rectification performed by the rectifying elements to the rectification performed by the switching elements. This smooth switching reduces a change in the output voltage.
Additionally in the present invention, an output current may be detected, and when the detected output current becomes larger than a threshold value, the switching pulse is gradually altered so as to gradually switch the rectification performed by the rectifying elements to the rectification performed by the switching elements.
According to the present invention, when the load is heavy with the large output current, the switching elements exhibiting a small on-state voltage enable an efficient current supply. When the load is light with the small output current, the rectifying elements, which do not switch, perform the rectification. The rectification performed by the rectifying elements prevents electric power loss resulting from undue switching, and enables an efficient current supply to a load, such as a CPU.
Additionally in the present invention, when the detected output current becomes smaller than the threshold value, the rectification performed by the switching elements may be immediately switched to the rectification performed by the rectifying elements.
According to the present invention, the immediate switching prevents an adverse current from a load, such as a CPU, immediately.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.